This application claims the priority of German patent document 101 29 457.3, filed 19 Jun. 2001 (PCT International Application No.: PCT/EP02/06479), the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for defining the time and scope of maintenance operations for a system having a plurality of maintenance items, each of which should be carried out within an associated flexible maintenance interval and tolerance range, with a predetermined minimum maintenance interval between successive maintenance operations.
Such methods are customary, for example, for the maintenance of motor vehicles. In this application, fixed maintenance intervals in the form of corresponding time intervals or mileage intervals are conventionally predefined. In addition, there is usually a fixed predefinition of which maintenance items are to be carried out during a respective maintenance operation. With this type of predefined maintenance of motor vehicles, the respective vehicle component is maintained at fixed intervals independently of the severity of its actual wear, which may vary appreciably from vehicle to vehicle, for example due to different driving styles.
German patent document DE 31 10 774 A1 discloses a method for defining maintenance times for motor vehicles in which a reference variable (for example, the state of the brake linings or the state of the engine oil), is fixed as decisive. An associated maintenance value of the reference variable is predefined and the actual value of the reference variable is sensed continuously while the vehicle is actually operating, and compared with the maintenance value. As soon as the actual value reaches the maintenance value, an indication is given that a maintenance operation should be carried out.
For further operating variables which are to be maintained as a function of wear, such as clutch, carburetor setting, spark plugs, ignition times and battery voltage, their actual values are also sensed from time to time and compared with stored wear limiting values. Depending on the wear state, the respective operating variable is assigned to a maintenance operation which is determined by the reference variable, within a tolerance range which is formed as a function of the mileage, fuel consumption, time or a combination of these variables. Here, the maintenance time is defined within the tolerance range in the direction of the upper or lower range limit by reference to an evaluation of the reference variable and the respective operating variable. In addition, assuming that loading of the vehicle remains the same, the wear limit can be extrapolated from a computing unit which carries out the method. A load diagram can be created for the operating variable values which are decisive for the loading of the vehicle, from which diagram it is possible to detect whether the vehicle is being operated mainly in the partial load mode or full load mode.
German patent document DE 32 34 727 A1 discloses a method for defining maintenance times for a motor vehicle in which the current wear of components that are to be maintained and the duration of operation or of the vehicle, the engine speed and the temperature of the cooling water are measured and the current wear is compared with a predefinable wear limiting value, in order to calculate the expected service life of the respective component therefrom. The shortest time period or distance in which a plurality of monitored components are subject to wear within a predefinable maximum tolerance range is then indicated, or the distance for a component which is worn by more than the predefined tolerance range before the other components is indicated.
One object of the invention is to provide a method of the type described above, with which the time and scope of maintenance operations can be defined for a system having a plurality of maintenance items in a comparatively reliable, flexible and cost-effective way.
This and other objects and advantages are achieved by the method according to the invention, in which, on the one hand, a minimum maintenance interval for a next maintenance operation (i.e., subsequent maintenance operation) and, on the other hand, flexible maintenance intervals and tolerance ranges for the maintenance items are predefined. The maintenance interval variable and the maintenance intervals and tolerance ranges for the maintenance items can be predefined differently. For the sake of optimization, it is possible to iterate over this variable maintenance interval.
Furthermore, at least some of the maintenance items are treated as serving to define maintenance times, and are referred to below as control function maintenance items. The latter are taken into account in defining the maintenance times. Specifically, for a particular maintenance operation which is to follow a preceding maintenance operation by at least a minimum maintenance interval, the time is predictively fixed at least at the earliest tolerance range end point (among the control function maintenance items) which complies with the minimum maintenance interval. All maintenance items whose tolerance end points occur before this predicted, aimed-at subsequent maintenance time are included in the extent of the preceding maintenance operation.
This procedure permits components which are subject to wear to be maintained sufficiently promptly, and thus reliably, in a very flexible way, by means of fixed or variable predefinition of the minimum maintenance interval and of the maintenance intervals and tolerance ranges which can be selected individually for each maintenance item. The maintenance intervals and tolerance ranges can be selected in a variable fashion as a function of the current conditions (in particular the current measured or predicted wear of the system component or components affected by a particular maintenance item), which permits a further improved adaptation of the subsequent maintenance operations to the current wear state of the various system components. In motor vehicles, different degrees of wear depending on the driving style can thus be taken into account in arriving at favorable maintenance times.
The method according to the invention thus ensures, on the one hand, that each maintenance item is carried out sufficiently frequently so that worn system components are maintained promptly, and, on the other hand, selecting a correspondingly long minimum maintenance interval avoids premature performance of maintenance operations.
In one embodiment of the invention, the maintenance items are categorized into one or more respective maintenance secondary items. When the sequence of a maintenance operation is created, the maintenance secondary items of the maintenance items which are to be processed in the maintenance operation are tested with respect to the possibility of combining them. This permits an effective maintenance sequence in which the maintenance secondary items are combined for processing in such a way that, as far as possible, each maintenance secondary item has to be carried out only once.
In another advantageous embodiment of the invention, an optimization algorithm is used in which the complexity of the maintenance serves as a so-called cost function which is to be optimized. The complexity of the maintenance may be enumerated here, for example, as a specific amount of money or a cost value.
It is possible to use maintenance positions (that is, the timing of maintenance items) with a control function which are extracted from the optimization algorithm in order to determine the maintenance time, while others are then merely added to the maintenance packages. It is possible to take into account fixed regulatory deadlines such as for TÜV[German standards testing authority], ASU[German exhaust gas test] and nonscheduled visits to the workshop. The optimization process also includes provisions for moving subsequent maintenance positions forward on a test basis (i.e., maintenance positions, which according to the normal criteria would not be due until a subsequent maintenance time), to a preceding maintenance operation. In this case, the predefined minimum maintenance interval functions as a secondary condition of the optimization process. This measure can be used to determine whether the performance of one or more maintenance items will lead to a lower overall degree of complexity and is therefore to be recommended.
In practice, the wear of components which are to be maintained may be subject to time intervals or distance intervals and be calculated from load collectives or sensor data. On a program-internal basis, calculations are preferably carried out only with one unit (time or distance) and the result can then be presented again in both units. The possibility of incorporating various models for determining wear for this purpose ensures that a framework algorithm is provided. This permits, inter alia, wear models of suppliers to be incorporated and tested. For reasons of practicability, the system preferably permits manual correction of the optimum solution, for example in order to achieve further, less than optimum, solutions with associated maintenance deadlines, extent and cost of maintenance, as well as subsequent maintenance deadlines and costs. The user can thus predefine the time period between two maintenance deadlines in a reasonable range and control weighting which is optimized to a greater extent in terms of cost or time.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.